next friend(n = noun.person) - (law) a person who acts on behalf of an infant or disabled person;
is a kind of agent

N  deputy, substitute, vice, proxy, locum tenens, badli, delegate, representative, next friend, surrogate, secondary, regent, viceregent, vizier, minister, vicar, premier, chancellor, prefect, provost, warden, lieutenant, archon, consul, proconsul, viceroy, commissioner, Tsung-li Yamen, Wai Wu Pu, plenipotentiary, alter ego, team, eight, eleven, champion, acting, vice, vice regal, accredited to, in behalf of.

best friend, friend, friend at court, friend of the court, girl friend, lady friend, next, next door, next of kin, next world